Oxygen sensors using a solid electrolyte body on which a catalytically active electrode and a catalytically inactive electrode are applied have previously been proposed.--see German Patent Disclosure Document DE-OS No. 2 547 683, based on U.S. application Ser. No. 524,674, Riddel. It has also been suggested that the solid electrolyte should be capable of being heated, typically being electrically heated. (see e.g. U.S. Pat. No. 3,597,345).
External heating of the solid electrolyte body of such a sensor has the advantage that it can be rendered active quickly and that its heating will not be dependent on the temperature of the gases, the oxygen of which it has to sense. Thus, the oxygen sensing capability can be obtained even upon cold starting of an internal combustion engine with which the sensor is used. An output signal can be obtained quickly. Heating the sensor has the additional advantage, specifically when used with automotive-type internal combustion engines, that lead is not precipitated on the sensor if the fuel used in the engine contains lead. Such lead has the tendency to precipitate on cold sensing elements. Heated sensors are particularly applicable and may be necessary where the exhaust gases must pass a substantial distance from the combustion chamber of the engine until they meet the sensor, for example in installations in which the exhaust gases from various cylinders of a multi-cylinder internal combustion engine can be combined only a substantial distance away from the cylinders. Heated sensors are especially useful and, indeed, may be necessary in opposed piston engines, in V-type engines, or the like, having separate exhaust manifolds for different cylinders or cylinder banks from which the exhaust gases are combined in a single exhaust duct.
Sensors which can be heated usually were so constructed that a separate heating winding was used to heat a solid electrolyte or a carrier therefor. In many instances the amount of heat which can be applied to the solid electrolyte or the carrier was insufficient so that the desired aim of rapid sensing capability of the sensor, and avoidance of precipitation of lead was achieved only partially and insufficiently. Yet, the additional heating winding caused additional costs and space for the sensor.